Technical Abstract:
Secondary metabolites produced in corn silks can promote resistance to caterpillar pests. We evaluated Hi-II corn plants engineered to express the P1 gene controlled by a putative silk specific promoter for secondary metabolite production and corn earworm resistance. Transgene expression did not enhance silk color, but 56% of newly emerged silks and 57% of mature silks displayed browning when cut, which indicates the presence of P1-produced secondary metabolites that are substrates of silk peroxidases. Levels of maysin, a secondary metabolite with insect toxicity, were present on average at 0.44% fresh weight (FW) in newly emerged silks and averaged 0.12% FW in mature silks compared to 0.008% FW and 0.002% FW in non-browning newly emerged and mature silks, respectively. Some transgenic kernels browned spontaneously, suggesting the promoter may not be silk specific or that genetic rearrangements occurred that conferred P1 expression in these kernels. The average mortality of corn earworm larvae fed newly emerged browning silks (61%) was not significantly different from the mortality of those fed newly emerged non-browning silks (53%). Mean survivor weights of corn earworm larvae fed mature browning silks (0.34 mg) were significantly lower than weights of those fed mature non-browning silks (0.39 mg). This information suggests P1 expression in silks can moderately enhance insect resistance in mature silks, and that maysin production promoted by P1 expression may be a contributing factor.